The invention relates to an arrangement for pneumatic false-twist spinning of the type having a drafting unit, at least one air nozzle which follows the drafting unit in the travel direction of the yarn, a withdrawal device, and devices for transferring the movably held air nozzle from an operating position behind a pair of delivery rollers of the drafting unit into a piecing position which is offset with respect to the pair of delivery rollers. A movably held suction tube is provided which can be brought into a piecing position by means of adjusting devices when the air nozzle is moved out of the operating position, in which piecing position the suction tube is applied to the area of the clamping gap of the pair of delivery rollers of the drafting unit.
An arrangement of the initially mentioned type is described in German Patent Application No. P 36 38 110.1, which is no prior publication and related pending commonly owned U.S. Pat. appication Ser. No. 07/108,218, filed Oct. 14, 1987, now U.S. Pat. No. 4,819,419. By means of this construction, a piercing process becomes possible, in which the drafting unit is restarted, before the start of the actual piecing operation, so that the piecing process is carried out even when the drafting unit is already running. The sliver, which was supplied by the drafting unit before the piecing operation, which possibly was not drawn correctly, is sucked off by means of the suction tube and does not enter the yarn. Only the sliver, which is sucked up by means of the air nozzles, which were returned to the operating position, is bound into the forming yarn. As a result, it is also possible to carry out the piecing without any returning of a yarn against the normal moving direction through the air nozzles into the area of the drafting unit.
An object of the invention is to simplify the construction and to provide an additional function to the suction tube which, during the whole operating period, was connected to a vacuum source.
This object is achieved in that, when the air nozzle is in the operating position, the suction tube is in a cleaning position, in which it is aimed at the circumference of one roller of the pair of delivery rollers of the drafting unit at a distance from the clamping gap.
By means of this construction, the suction tube is disposed at a sufficient distance from the clamping gap during the operation, without having to carry out an excessively large movement. The sucking-up of fibers is therefore avoided. At the same time, it carries out a cleaning function.
In a further development of preferred embodiments of the invention, it is provided that the suction tube is arranged on a holder and can be swivelled between the piecing position and the cleaning position. This type of a swivelling holding arrangement is particularly easy to implement.
In a further development of the invention, it is provided that the suction tube is coupled with the air nozzle in such a manner that it follows the movement of the air nozzle such that, when the air nozzle is located in the piecing position, the suction tube is also located in the piecing position. It is therefore sufficient to provide adjustable actuating devices only for the air nozzle, while the suction tube is taken along automatically into the respective position.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.